SUMMARY Proper development of gametes is crucial for the continuation of sexually reproducing species. To succeed, germline stem cells that populate the gonads must complete a long developmental process that yields highly differentiated cells: the sperm and egg. These can come together to form a totipotent zygote capable of developing into an individual. Thus far, genetic screens in mice, flies, and nematodes, have identified numerous genes required development of the germline. However, voids remain to be filled in our understanding of the genetic mechanisms that secure the production of functional gametes. To fill some of these voids, the proposed line of research will explore a new avenue for discovery of genes involved in germline development. The planarian flatworm Schmidtea mediterranea is an increasingly popular organism for stem cell research, which holds great promise as a model for reproductive biology studies. Planarians have an unmatched ability to completely regenerate their entire reproductive system, including germ cells, throughout their lifetime. This allows experimental analysis of the entire process of gametogenesis without being confined to a specific developmental window, or limited by potential secondary effects on embryogenesis. Also relevant is the fact that planarians specify their germline through inductive signals that originate from the soma, which is also true of mammals (but not of flies or nematodes). Experiments performed as part of this proposal are expected to reveal conserved pathways that control germ cell development by: 1) Elucidating the structure and function of cytoplasmic ribonucleoprotein granules that regulate spermatogenesis intrinsically; 2) Uncovering the identity and fate of mRNA targets of these granules through association with the highly-conserved Cytoplasmic Polyadenylation Element Binding Protein-2; and 3) Identifying components of genetic pathways involved in non-cell autonomous (i.e. extrinsic) regulation of germline development. Due to availability of optimized protocols for assessing distribution of gene expression in planarians, ease of maintenance and induction of systemic knockdown, as well as availability of molecular markers for virtually every tissue, the expression and function of dozens of genes can be determined during the award period by research performed in large part by undergraduate students. Completion of this project is important because it will reveal conserved processes involved in development of functional gametes. Additionally, this work will expose hundreds of undergraduate students to meritorious research, and strengthen the research environment at Wright State University, which are specific goals of the AREA program.